I stressed the point with him - as I thought this was the mistake he was making and still think it is what has happened.
jeremy
Xantia brake pedal pulsing
Moderator: RichardW
Hello again,
This is driving me round the twist!!
Earlier on I was braking and there was no pulsing (which happens now and then!) and I noticed the ABS light came on, as this happened the pulsing started again. There were no cars behind so I pressed the brake hard and the O/S/F wheel locked up.
What do you suggest I try next? - I know you have commented on my point below before, but I am becoming confused with it all.
<ul><li> </li><li> </li><li> </li></ul>Could this be a faulty ABS sensor or wire?
<ul><li> </li><li> </li><li> </li></ul>Could it be air in that part of the braking system which also makes the pump kick in and out?
I have spoken to a Citoen secialist and they told me that they had a similar problem with a Xantia and it was the brake dozer valve but it may not be the case with my car.
<ul><li> </li><li> </li><li> </li></ul>Do I go for a new brake dozer valve?
I <u>WILL</u> get to the bottom of this if it's the last thing I ever do!!!!!
Regards,
Mark
This is driving me round the twist!!
Earlier on I was braking and there was no pulsing (which happens now and then!) and I noticed the ABS light came on, as this happened the pulsing started again. There were no cars behind so I pressed the brake hard and the O/S/F wheel locked up.
What do you suggest I try next? - I know you have commented on my point below before, but I am becoming confused with it all.
<ul><li> </li><li> </li><li> </li></ul>Could this be a faulty ABS sensor or wire?
<ul><li> </li><li> </li><li> </li></ul>Could it be air in that part of the braking system which also makes the pump kick in and out?
I have spoken to a Citoen secialist and they told me that they had a similar problem with a Xantia and it was the brake dozer valve but it may not be the case with my car.
<ul><li> </li><li> </li><li> </li></ul>Do I go for a new brake dozer valve?
I <u>WILL</u> get to the bottom of this if it's the last thing I ever do!!!!!
Regards,
Mark
Mark -
Your brake test resulting in 1 wheel locking - tells you :
1) Basically the brakes are working (doseur valve fine).
2) The ABS system did NOT prevent locking the locked wheel, as it's supposed to do.
If you have a failing wheel sensor, the whole ABS system will be shutdown, and the ABS warning will light up. The ABS valve block has a separate valve to each front wheel's brakes, and 1 common valve to the rear wheels brakes. It's clear from your test, that (at least) one front wheel valve did not operate as it should.
In my opinion you should try trace down the reason why the valve for the wheel in question did not operate.
I'd try go for the following (easy done) :
Have engine idle, set to HI height (for rear bleed), apply handbrake, press the brake pedal clamping a piece of wood between pedal & drivers seat.
1) Bleed the brakes, ALL wheels [:0]
2) If ANY bleed screws seen on brake cylinder/ABS valve block - bleed these.
3) Stop engine, remove + cable from battery (Important [B)]). Check wiring/connector to/on ABS valve block. Be sure - do'nt accept even minor slop - the valves consumes heavy currents - requires heavy gauge & good quality wiring/connectors.
4) Check the ABS valve block's electric coils for continuity.
Schematic diagrams may be found here :
http://citroeny.cz/servis/servis.htm
5) Rarely, but still possible - you may simply have a defective ABS valve block (1 of the coils defective, i.e burnt/open circuit). The ABS ECU checks the coils & wirings for continuity, and also have overload sensors, if the coil/wiring is shortcircuited. This will of course also light up the ABS warning.
6) Check wheel sensors & wiring (still : battery + disconnected !). Several connectors are found in the wiring, easy to find a testpoint. Check resistance out in the sensors.
Your brake test resulting in 1 wheel locking - tells you :
1) Basically the brakes are working (doseur valve fine).
2) The ABS system did NOT prevent locking the locked wheel, as it's supposed to do.
If you have a failing wheel sensor, the whole ABS system will be shutdown, and the ABS warning will light up. The ABS valve block has a separate valve to each front wheel's brakes, and 1 common valve to the rear wheels brakes. It's clear from your test, that (at least) one front wheel valve did not operate as it should.
In my opinion you should try trace down the reason why the valve for the wheel in question did not operate.
I'd try go for the following (easy done) :
Have engine idle, set to HI height (for rear bleed), apply handbrake, press the brake pedal clamping a piece of wood between pedal & drivers seat.
1) Bleed the brakes, ALL wheels [:0]
2) If ANY bleed screws seen on brake cylinder/ABS valve block - bleed these.
3) Stop engine, remove + cable from battery (Important [B)]). Check wiring/connector to/on ABS valve block. Be sure - do'nt accept even minor slop - the valves consumes heavy currents - requires heavy gauge & good quality wiring/connectors.
4) Check the ABS valve block's electric coils for continuity.
Schematic diagrams may be found here :
http://citroeny.cz/servis/servis.htm
5) Rarely, but still possible - you may simply have a defective ABS valve block (1 of the coils defective, i.e burnt/open circuit). The ABS ECU checks the coils & wirings for continuity, and also have overload sensors, if the coil/wiring is shortcircuited. This will of course also light up the ABS warning.
6) Check wheel sensors & wiring (still : battery + disconnected !). Several connectors are found in the wiring, easy to find a testpoint. Check resistance out in the sensors.
Akojic, as I said, dosieur valve / brake valve / brake dosieur valve (or whatever) is under (and behind) the LHM tank on LHD Xantia models. Of course, it is not directly connected with it, like in conventional braking system, it gets the pressure from the regulator via the securtity valve (front brakes) and rear suspension (rear brakes). Other 2 pipes lead to front and rear brakes.
Of course, on RHD models (UK), brake pedal is on the opposite side, so is the dosieur valve - it's behind the engine in that case.
Of course, on RHD models (UK), brake pedal is on the opposite side, so is the dosieur valve - it's behind the engine in that case.
-
blueboy2001
- Posts: 423
- Joined: 29 Jan 2003, 04:16
- Location:
- My Cars:
Changing a Brave Valve is an absolute pain in the backside to do, I would not go changing it unless you're convinced thats the root of the problem, in my case despite all the symptoms being present it made not a jot of difference. The design of the valve is pretty much bomb proof, and the only way I could see any sort of considerable wear occuring would be if the LHM had a lot of rubbish in it and caused irregular wear. I'm sure it was AlanS who said more good brake valves get replaced than bad ones, I can see what he means.
If you do decide that it is the problem, then be prepared for some skinned knuckles. Now your valve will be on the opposite side of the car, so access will be completely different. On mine we had to remove all the rigid plastic air piping, the rocker cover and some coolant hoses.
If you do decide that it is the problem, then be prepared for some skinned knuckles. Now your valve will be on the opposite side of the car, so access will be completely different. On mine we had to remove all the rigid plastic air piping, the rocker cover and some coolant hoses.
-
ghostrider
- Posts: 360
- Joined: 05 Jan 2002, 01:10
- Location: United Kingdom
- My Cars:
- Contact:
Mark, just a thought the front wheel locking definitely sound like an itermittent ABS fault and Anders has pretty well covered that, Have you checked the condition of the Discs? I had one develop a crack running from the centre out to the outer edge of the disc, everytime I put my foot on the brake you got a pulsing sensation through the pedal as the disc was not only cracked but slightly warped as well. mind you I see that you say it happens when stationary as well.........
________
Ultimate fighters
________
Ultimate fighters
Last edited by ghostrider on 22 Feb 2011, 05:26, edited 1 time in total.
-
norfolkmick
- Posts: 6
- Joined: 12 Jul 2003, 20:24
- Location: United Kingdom
- My Cars:
My 1993 Xantia LX TD non abs has the same pulsing brakes and the pump kicking in to quickly. I've replaced the pump, had two new accumulators, S/H flow distributor, S/H regulator, I've stripped the regulator and reseated the ball and it still pulses.
Most of my troubles are because the car has had a very hard life, the filters in the reservoir were as black as an oil filter. I've flushed the system twice.
I can only think the problem is in the brake valve or the yet to be found security valve.
Can any body tell me where the bleed nipple is on the brake valve, I'll try that next.
Please help.
Desperate Mick
Most of my troubles are because the car has had a very hard life, the filters in the reservoir were as black as an oil filter. I've flushed the system twice.
I can only think the problem is in the brake valve or the yet to be found security valve.
Can any body tell me where the bleed nipple is on the brake valve, I'll try that next.
Please help.
Desperate Mick
There's no bleed nipple on the latest type of the brake valve (introduced with XM), only a 'calibrating plug' (for rear brakes).
Akojic replaced brake valve about a month ago and reported (in Croatian Citroen forum) that it cured pulsing of rear brakes, as well as fast sinking of rear end. Hope he can tell you more.
Akojic replaced brake valve about a month ago and reported (in Croatian Citroen forum) that it cured pulsing of rear brakes, as well as fast sinking of rear end. Hope he can tell you more.
Mick -
It may well be the brake valve -
A known procedure is to check for flow in return hoses from the hydraulics.
IIRC the brake valve has 2 return hoses attached - try follow these hoses to find a point where they easy unplugs - then check for any flow with engine idle - normal height - NO actuators touched.
Ultimately you may prepare a couple of connecting pieces for connecting 2 hose ends - then cut these hoses to test the flow. They only carry return pressure when brakes released.
Added :
The safety/priority valve is a smallish hydraulic component - with 4 rigid pipes connected, 1 wire attached for low pressure warning lamp & a return hose for overflow to reservoir.
One of the rigid pipes is 4.5mm directly running from regulator - the other pipes are 3.5mm pressure feeds to brake valve & suspension.
Try follow the 4.5mm pipe from regulator - and you should find the safety valve.
I don't think the safety valve can be your problem.
It's a very simple device - never heard of one in need for replacing.
It has 1 simple valve function :
When the pressure at engine start is low - the valve is in rest position - blocking off pressure feed to suspension - in favour of pressure to the brakes, which is ALLWAYS connected.
If the system is working properly (no leaks) - the pressure will rise and at approx 90bar the valve opens for pressure feed to suspension.
The valve simply ensures that suspension does not "eat" up pressure - ensuring that the brakes gets working pressure first.
It may well be the brake valve -
A known procedure is to check for flow in return hoses from the hydraulics.
IIRC the brake valve has 2 return hoses attached - try follow these hoses to find a point where they easy unplugs - then check for any flow with engine idle - normal height - NO actuators touched.
Ultimately you may prepare a couple of connecting pieces for connecting 2 hose ends - then cut these hoses to test the flow. They only carry return pressure when brakes released.
Added :
The safety/priority valve is a smallish hydraulic component - with 4 rigid pipes connected, 1 wire attached for low pressure warning lamp & a return hose for overflow to reservoir.
One of the rigid pipes is 4.5mm directly running from regulator - the other pipes are 3.5mm pressure feeds to brake valve & suspension.
Try follow the 4.5mm pipe from regulator - and you should find the safety valve.
I don't think the safety valve can be your problem.
It's a very simple device - never heard of one in need for replacing.
It has 1 simple valve function :
When the pressure at engine start is low - the valve is in rest position - blocking off pressure feed to suspension - in favour of pressure to the brakes, which is ALLWAYS connected.
If the system is working properly (no leaks) - the pressure will rise and at approx 90bar the valve opens for pressure feed to suspension.
The valve simply ensures that suspension does not "eat" up pressure - ensuring that the brakes gets working pressure first.